TREMATODA 49 



b. Shape, oval, considerably longer than wide. 



1. Somewhat barrel shaped; with plugs at each end. 



Trichuris trichiura (Plate V, Fig. 16). Color 

 of eggs dark brown; 50/i to 57/x by 23ju; ovum 

 unsegmented. 



2. Thick transparent shell with an external albu- 



minous coating which forms protuberances. 

 A scaris lumbricoides (Plate V, Figs. 13, 14, 15). 

 Color of eggs brown; 50/i to 70/* by 40ju to 5(V; 

 ovum unsegmented. 



3. Asymmetrical, flattened on one side. 



(a) Enterobius vermicularis (Plate V, Fig. 19). 



Color transparent; contains tadpole like 

 embryo ; size of egg 5(V to 55/* by 16/* to 

 24/i. 



(b) Oxyuris incognita (Plate V, Fig. 20). Oil 



globules at each end of egg; average size 

 of egg OOM by 40/z. 



4. Shell thin, transparent; embryo in four to many 



cell stages. 



(a) Trichostrongylus orientalis (Plate V, Fig. 



21). Ends somewhat pointed; size 75/t to 

 90 M by 39 M to 47/i. 



(b) Necator americanus. Size 58/x to SO/* by 



35/t to 52/z. 



(c) Ancylostoma duodenale (Plate V, Figs. 17- 



18) . Size 56jit to 61/* by 34/i to 38/x. 



4. TREMATODA 

 A. Definition 



Parasitic Platyhelminthes ; cilia present only in larval 

 stage; adults always covered with cuticula; suckers present 

 for attachment; digestive system without anus, usually 

 bifurcated; development by metamorphosis or alternation 

 of generations; adults parasitic in vertebrates. 



